As for a damper comprising a piston and a cylinder storing the piston, and generating a braking force based on a movement or relative movement of the piston, there is a damper disclosed in Patent Document 1.
In such a damper, while generating the braking force when the piston moves forward in a direction of extending a pressure chamber, the piston can move backward in a direction of reducing the pressure chamber with a small resistance.
Namely, in the Patent Document 1, at a time of the aforementioned forward movement, an outer peripheral portion of a seal ring 300 surrounding an outside of a piston 100 slidingly contacts an inner wall of a cylinder 200, and an inner peripheral portion of the seal ring 300 contacts a trunk portion 101 of the piston 100 (see FIG. 11). On the other hand, the seal ring 300 can move in the trunk portion 101 of the piston 100 within a predetermined range along a moving direction of the piston 100, and at a time of the aforementioned backward movement, the seal ring 300 moves in a direction of separating from a pressure chamber 400 so as to position the inner peripheral portion thereof on a ventilation groove 102 formed in the trunk portion 101 of the piston 100 (see FIG. 12). Thereby, at the time of the backward movement, the backward movement can be carried out by an exhaust air from the pressure chamber through the ventilation groove 102 with the small resistance.
However, in the Patent Document 1, the exhaust air at the time of the backward movement remains to a limited one through the ventilation groove 102, and in order to ensure such exhaust air, the seal ring 300 is required to move the inner peripheral portion thereof up to a position located above the ventilation groove 102, and it is structurally incapable of ensuring the exhaust air without a time lag at the same time of starting the backward movement. Also, for example, in a case of being applied to buffering of an opening operation of an opening and closing member such as a glove box of an automobile and the like, in the time lag of the exhaust air, when a force in an excessive opening direction is applied to the opening and closing member such as the glove box and the like, a force in a direction to close the opening and closing member is generated in the opening and closing member by a sharp increase of an inner pressure of the pressure chamber, so as to cause a rebound of the opening and closing member in a closing direction unintended by a user, i.e., a rebound phenomenon.